constraints order

[Michel Levy]

I do not understand why these two requests have different answers :
| ?- X #\=Y, X #=Y.
X = _#2(0..268435455)
Y = _#21(0..268435455)
| ?-  X #=Y, X #\= Y.
no.
This contradicts the assumption that the order of the constraints is 
unimportant.

Furthemore, in the official documentation, I read :
fd_all_different(List) constrains all variables in List to take distinct 
values. This is equivalent to posting an inequality constraint for each 
pair of variables.

But this equivalence is no true :
| ?- X #=Y, fd_all_different([X,Y]).
X = _#0(0..268435455)
Y = _#0(0..268435455)
yes

Can you explain me the difference ?

--
Michel Levy
Laboratoire L.S.R., Bureau C214, B.P.72 - 38042 SAINT MARTIN D'HERES CEDEX
e.mail : address@hidden    tel :(33)476514022
http://www-lsr.imag.fr/users/Michel.Levy